Photo: Philadelphia 76ers/Twitter

When it mattered the most, James Harden turns back the hand of time.

Channelling his vintage scoring machine form, Harden charged the Philadelphia 76ers over the Boston Celtics, detonating for 45 points – tying his playoff career-high – in the club’s 119-115 Game 1 East Semis statement dub on Monday night in TD Garden.

With 8.4 seconds to go, Harden buried a clutch signature, step-back three-pointer over Al Horford to fully maneuver the 76ers towards second-round series opener victory – icing a classic performance with presumptive MVP Joel Embiid sitting out because of a knee injury. He shot 17-of-30 from the field and also grabbed six boards.

Harden’s 15 of his 45 markers served as the engine of Philly’s fourth-quarter rally. Together with Tyrese Maxey, who had 26 points and four steals, they led the 76ers’ 12-4 run to close out the match.

Paul Reed, the 76ers’ seldomly used backup big, emerged pivotal to aid his team down the stretch, draining two clutch free throws to fully lift themselves over the C’s for a four-point road win.

As he dropped a 45-point masterpiece, Harden joins ex-Philadelphia cornerstone Allen Iverson as players who managed to drop 45 markers in a playoff game for the past 50 years in the franchise’s history (h/t StatMuse).

Jayson Tatum came up big on a losing effort, churning a team-high 39 points, 11 rebounds and five assists. Jaylen Brown, for his part, poured an efficient 23 points, six rebounds and four assists.

Per ESPN’s Stats & Info, this marks the ninth time this season that the Celtics have crumbled as a double-digit favorite, the most by any team in a single season since 1990-91.

With Philadelphia taking an early series upperhand, Boston will stage Game 2 on Wednesday.